Mechanical construction of loud speakers



Nov. 1, 1932; R. H. LANGLEY MECHANICAL CONSTRUCTION OF LOUD SPEAKERSFiled Jan. 19, 1931 4 Sheets-Sheet 2 gNVENTOR. w ATTORNEYS Nov. 1, 1932R. H. LANGLEY MECHANICAL CONSTRUCTION OF LOUD SPEAKERS Filed Jan. 19,1951 4 Sheets-Sheet 1 2 nwgrok. v

A TTORNEY$ Nov. 1, 1932. R LANGLEY 1,886,031

MECHANICAL CONSTRUCTION OF LOUD SPEAKERS Filed Jan. 19. 1931 4Sheets-Sheet 5 I N VEN TOR.

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ATTORNEYS Nov. 1, 1932.

R. H. LANGLEY MECHANICAL CONSTRUCTION OF LOUD SPEAKERS Filed Jan. 19,1931 4 Sheets-Sheet 4 A TTORNEYJ Patented Nov. 1, 1932 UNITED STATESPATENT OFFICE RALPH H. LANGLEY, OF CINCINNATI, OHIO, ASSIGNOB TO THECBOSLE'Y RADIO CORPORATION, OF CINCINNATI, OHIO, A. CORYORATION OI OHIOMECHANICAL CONSTRUCTION OF LOUD SPEAKERS Application filed January 19,1931. Serial Iio. 509,555.

My invention relates to improved types of loud speaker motors, and whileit is applicable to motors in which the field flux is furnished by apermanent ma net or magnetic system, the specific embo iment which Ishall describe in making a disclosure of my invention, will be a type ofmotor in whic the field is electro-magnetic.

The elements ofa loud speaker motor ema n bodying the principles which Ishall hereinthe exemplary speakerwhich I shall herein describe. Myinvention has to do with the mechanical construction of this speaker;that is to say, the mechanical embodiment, form, assembly, andconstruction of the parts, together with a method of fitting andassembling the same, as distinguished from the operative elements of thesaid speaker which may be embodied in the said construction.

As Will be pointed out hereinafter, certain phases of my invention willbe applicable to other types of motors. The inherent novelty in myinvention I have set forth in the appended claims. In making adisclosure of my invention in a specific embodiment I shall describe theconstruction described by the said Hunter and Rockwell, and in orderthat the operativeness of my specific embodiment may be more readilyunderstood I have also explained hereinafter the operation of the saidspecific embodiment.

It has been one of my objects to simplify the construction and decreasethe cost of loud speaker motors, and I have succeeded in constructing amotor in accordance with the following disclosure at a commercial costmaterially beneath'the cost of any other commercial loud speaker ofwhich I am aware.

It is another of the objects of my invention to provide a mechanicalconstruction which greatly simplifies the assembly of the motor,

and which is variable to the extent of permitting the motor to be usedwith various elements and with varying numbers of elements, as will beset forth hereinafter more fully in connection with a description of the5 operation of the exemplary motor to which my invention has beenapplied in the ensuing disclosure. 3

The objects of my invention will be set forth in detail hereinafter, orwill be entirely apparent to one skilled in the art upon reading thesespecifications, and reference is now made to the drawings, in whichFigure 1 is a diagrammatic perspective representation of the parts ofthe speaker embodying my invention.

Figure 2 is also a diagrammatic representation showing the relationshipof the armature and the magnetic bridge portions to the poles of myfield structure.

Figure 3 is a diagram in which magnetic flux 1s lotted against currentto show the approac to a condition of magnetic saturation.

Figure 4 is a scale drawing showing in plan one of the laminations of afield element.

Figure 5 is an edgewise view of an assembled field element.

Figure 6 is an elevation thereof.

Figure 7 is a plan view-of one of my supporting brackets.

Figure 8 is a side elevation thereof.

Figure 9 is an end elevation of the same bracket.

Figure 10 is a side elevation of an assemb1y of my brackets and thefield element of Figs. 5 and 6.

Figure 11 is an end elevation of the same structure.

Figures 12, 13 and 14, are respectively side and end elevations and atop plan view of one of the elements forming the return magnetic path ormagnetic bridge circuit of my apparatus.

Figure 15'i'san end elevation.

Figure 16 is a side elevation of one of my voice coil structures.

Figure 17 is a side elevation.

Figure 18 is an end elevation of one of 1m my spring retaining devicesfor the voice coils.

Figure 19 is an elevation of my armature and the attached driving rod.

Figure20 is a plan view of myarmature.

Fi re 21 is an end elevation of a complete motor.

Fi ure 22 is a top plan view of a complete motor.

Figure 23 is a sectional view of a motor taken along the lines23, 23 ofFig. 22.

F i re 24 is a side elevation of my complete motor.

Figure 25 is a sectional view of my motor taken along the lines 25, 25of Fig. 24.

One of the objects of my invention has been to produce in a magneticarmature type speaker, an economical construction in which a return athis provided for the alternating or uctuating flux in the armature, whichpath is not co-extensive with the path of the flux in the fieldstructure. Accordingly, I have devised, as will fully be ex-- lained, astructure in which the return path ibr the armature flux is in astructure lying essentially in a plane transverse to the plane of themain field structure. As has been understood by investigators in thisfield, one of the disadvantages of the magnetic type of loud speaker hasbeen the permeation of the field structure by the alternating fluxproduced in the armature.

Another well known disadvantage of the magnetic type speaker has beenthe saturation of the armature with the magnetic flux produced by thefield, and it has been an other object of my invention to provide anadequate and economical construction in a magnetic type speaker in whichthe armature is practically free of magnetic saturation due to thefield.

Due in part to the foregoing disadvantage, viz., the saturation of thearmature by the field flux, but also aflfected by other factors, thearmature of magnetic type speakers has been less readily able to givesatisfactory reproduction of impressed si als because it is in a stateof relative un alance upon movement; that is to say, the closer thearmature approaches either pole of the field, the more strongly it isattracted to the said pole and so great is the increase in thisattraction upon movement that the motion-response to thevariations inthe armature actuation current is no longer true. The response of such amotor is essentially non-rectilinear; and it is an object of myinvention to produce, and I have succeeded in producing a motor theresponse of which is much more nearly rec tilinear.

The essential features of the exemplary motor to which my invention isapplied are set forth diagrammatically in Figure 1, wherein I have showna field structure comprising a core of essentially C shape, and

having a back portion 1, side portions or legs 2 and 3, and oppositeportions on the oppo-.

derstood that this armature is mounted in suitable supports at its endsand is free to vibrate in its central portion, which is the portionlocated between the pole pieces N and S. A field coil 6 has beenindicated diagrammatically as situated upon the back portion of thefield core structure. When this coil is energized by direct current; thefield core structure will be magnetized and permeated by a constantflux. It may be so magnetized that the pole pieces marked N and S willbe respectively the north and south poles of the magnetic structure, theflux across the air-gap 4 passing through the central portion of thearmature 5. I have indicated diagrammatically voice coils 7 and 8 uponthe portions of my armature 5 which extend beyond the air-gap. Thesecoils are connected in series, but are wound in the opposite directionso as to have an opposite magnetic effect upon the central portion ofthe armature. These coils are intended, of

course, to be energized by a voice current of fluctuating or alternatingcharacter. The passage of this current in one direction will tend tomagnetize the armature with a north pole at its center, while thepassage of the current in the opposite direction will tend to magnetizethe armature with a south pole at its center. A loud speaker motorconstructed merely as just'describ'e'd would be operative, but itsefiiciency would be relatively low because there would not be any closedmagnetic circuit for the alternating flux set up in the armature. Afeature of the construction is the provision of'means for completing themagnetic circuit for the armature flux, and in the preferred embodimentillustrated in Figure 1, I have shown magnetic bridge arms or by-passpath constructions 9, 10, 11 and 12. These arms connect the pole piecesN and S with the outer ends respectively, of the armature. Theirfurliction will now be explained more in detai I have shown in Figure 2the pole pieces N and S with the armature 5 lying in the air-gap 4between them. The armature is connected by a suitable drive rod 13,passing through a perforation 14 in the pole piece N and connecting thearmature either tion, and the voice coils have been indicated at 7 a andSo. When the-field structure is actuated by a suitable direct current,there will be a flux in the pole pieces N and S and across the air-gap 4in the direction of the arrows in Figure 2. The arms 9 to 12 aremagnetic arms, and as respects the field flux, the arms 9 and 10 uponthe one side and the arms 12 and 11 upon the other act as magneticby-passpaths for the field flux, and" they will be saturated with amagnetic flux in the direction of the arrows. It is desirable to havethenr saturated as aforesaid, and for this reason they are made ofrelatively light magnetic material. They may be made of thick material,but the o eration of my speaker will not be entire y the same as thatwhich I shall presently describe; and although good speakers may be madethis way, the relationship of parts 1s very much more exact and hard toobtain than if the paths are made relatively llght and are keptsubstantially saturated. In Figure 3 I have, by way of example, plottedflux against current to produce a curve 16, showing the degree ofmagnetic saturation in one of the arms. It has been found preferable soto proportion the size of the arms with relation to the size of thefield structure and the flux therein, that the arms will be operated atsome point high up on the saturation curve, such as the point 17.

In considering the operation of this speaker, the arms 10 and 11 may befirst considered. If the coils 7a and 8a are magnetized by a currentwhich tends to produce anorth pole at the center of the armature, thedirection of the flux in the armature will be that of the small arrowswithin the ends thereof. A flux flowing inwardly in the left hand end ofthe armature must take as its return path, the pole piece S and the arm11. The arm 11 is saturated in the direction of the arrow, and thereforeis a very low reluctance path.

( Flux flowing inwardly in the right hand end of the armature must takea path embracing the arm 10 and the pole piece S. The arm 10 issaturated in the direction of the arrow; but the direction ofthe flux inthe armature is opposite to this and therefore can flow in the arm 10over a relatively low reluctance path opposite in direction to thedirection of saturation therein. Thus a mag netic circuit for thearmature flux is presented by the right hand end of the armature, thepole piece S and the arm 10. The central portion of the armature is morestrongly magnetized as a north pole, and is repelled from the pole pieceN and attracted to the pole piece S. I

If there were in Figure 2 no arms 10 and 12, it is clear that thearmature would be permeated and perhaps saturated by the field flux,since there would be a ma etic clrcuit between the pole pieces N andcomprising in sequence, the arm 9, the armature, and the arm 11. Amagnetic s eaker of some efliciency can be made in is way, and itsoperation is vastly improved over that which results when no returnpaths are provided for the armature flux. The situation which has beendescribed for one direction of the alternating voice coil current will,of course, be reversed for the other alternation; and if the directionof the current in the voice coils 7a and 8a tends to magnetize thearmature with a south pole at its center, there will be presented to thearmature flux a high reluctance ath comprising the arm 11, and a highreuctance path comprising the arm 10.

Now, when there is added to this system the arms 10 and 12 severalresults are accomplished. Since the arms 9 and 10 on the one side andthe arms 12 and 11 on the other form magnetic by-pass paths for thatportion of the field flux which they can carry up to their point ofsaturation, and since the armature is connected between these by-passpaths, there is produced a balanced magnetic bridge circuit, in whichthe armature is substantially unsaturated by the field flux, in whichthe production of an alternating flux in the armature is not modified byany substantially resident magnetic permeation in the armature, and atwhich magnetic circuit return paths for the alternating flux in bothends of the armature are provided. It will be noted also, that themagnetic circuit or circuits for carrying the alternating flux of thearmature are in a plane diiferent from the plane of the field core, andthat there is substantially'no tendency for the field core to carry thealternating flux produced in the armature.

Let it be supposed that the action of the coils 7 a and 8a is to producea north pole at the center of the armature 5 in Figure 2. In accordancewith the foregoing explanation, it will be clear that the-re will bepresented to this flux relatively high reluctance return pathscomprising arms 9 and 12, and relatively low reluctance return pathscomprising arms 10 and 11. Upon the passage of the current in theopposite direction, i. e. so as to magnetize the armature with a southpole at its center, the paths embracing the arms 9 and 12 will be lowreluctance paths, and the paths embracing the arms 10 and 11 will behigh reluctance paths. Since the flux flows in the low reluctance pathsessentially by bucking a saturation flux therein, it will be clear thatthis construction provides shifting balance points for the armature,lying out upon the several arms. The function of the return paths instrengthening the arma-' ture fiux will be apparent, and the repulsiveand attractive forces acting upon the armature at its central portionwill, of course, produce in it the vibrations which are transmitted bythe drive rod 13 to the vibratile device 15 in reproducing sound. Thearmature is substantially not permeated by the field flux, and itsresponse to fluctuations of the armature Current is not only true, butpowerful. Hereinabove I have described a motor of the Hunter andRockwell type as operating with what I have termed. a strip formarmature, with either a pair of magnetic arms connecting the ends of thearmature respectively with the pole pieces N and S, or with a pluralityof magnetic arms completing the magnetic circuits, as shown in Figure 2.There is another modification which has been found to give excellentresults, and which has an economical-advantage. In this modificationinstead of employing a strip form armature, there is employed what maybe called a reed form armature, i. e. an armature which is mounted atone end only, the other end being free to vibrate. Such a constructionmay be understood from Fig. 2 if, for example, the magnetic arms 9 and10 are eliminated, the voice coil 7 a taken away, and the armature 4 cutoff, say, close to the right end edges of the pole pieces N and S. Thearmature will then be in the form of a reed mounted at its left-hand endbetween the magnetic arms 11 and 12. It will be magnetized by the voicecoil 8, as has been described and the operation of this modificationwill be essentially the same as that which has been described for othermodifications. A return ath for each of the magnetic paths produce bythe fluctuations of the alternating current will comprise respectivelythe armature, the magnetic arm 12, and the pole piece N for one path,and the armature, the magnetic arm 11, and the pole piece S for theother path. There is greater necessity in this modification for carefulproportioning of the armature, and it will be advisable to provide anarmature, where possible, the natural period of which it outside theaudible range. In speakers of the reed type constructed in this way, Ihave secured very excellent results and very true reproduction.

I will proceed now to the construction of the exemplary commercialspeaker embodying my invention in its several parts. I have shown inFigure 4 a stamping forming a lamination of my core. For convenience inassembling my motor, as hereinafter to be described, I make my core intwo pieces, which are afterward put together to form my completed core.The laminations 18 of Figure 4 are provided with suitable holes and areput together to form the core members 18a of Figures5 and 6. Thelaminations may be assembled by means of rivets 19. The front portion Nof my core members 18a may conveniently be made a little wider than therear portion, as shown, and the perforation 14 may be made therein forthe passage of the drive rod. The core member may also be provided withperforations 20- and 21 for purposes presently to be described. For eachmotor I make up two of these core pieces, only one of which, however,need have the perforation 14'. I also provide in the portion msiilrkedN, shoulders 22 to hold the voice co s.

As shown in Figures 7, 8, and 9, I provide bracket members ofnon-magnetic material adapted to be attached respectively to my corepieces 18a, and to each other. These brackets I have been making of castaluminum, but other non-magnetic materials will serve. They comprise abody portion having parts 23 and 24 extending at right angles. The part23 has a flange portion 25, and the part 24 has another flange portion26. The flange portion 25 may be provided with perforations 21a, wherebyit may be fastened to one of my core members. A reinforcing ribstructure 27 may join the flanges 25 and 26 across the body of mybracket, and this rib structure may be provided with a boss 28perforated and threaded as at 29 for the reception of a screw in holdingmy motor to a suitable support. The flange member 26 has a projection26a upon one end to hold the armature in the magnetic arms. The flangemay have perforations 30 for the reception of bolts in assembling mymotor. A pair of these brackets is assembled with a core member 18a insuch a way that the flange 25 is attached by means of rivets 31, passingthrough the perforations 21a in the flange and 21 in the core member,the portion N extending beyond th'bracket, as shown in Figure 10, andthe flange portions 26a extending out opposite the portion N and lyingin a plane at right angles to the plane of my core piece. I can take theassembly shown in elevation in Figure 11 and grind it, or otherwisedress it, until the faces of the flanges 26 and the ends of my corepiece lie in the same plane. In

building up my motor, I take two of the assemblies shown in Figure 11and fasten them together, with the respective flanges 26 contiguous andparallel, and it will be clear that by introducing spacers between theflanges 26, I can space my core members to the extent of producing anair-gap of the desired width.

I have shown in Figures 12, 13 and 14, one of the magnetic arm members,it has a body portion 32, and flange portions 33 and 34, one of which isprovided with notches 35, and the other with an attachment perforation36. In assembling my motor, I position two of the assemblies of Figure11 in opposite relationship, as aforesaid. This is illustrated in theside elevation of Figure 24 where the opposed flanges 26 are shownattached together, as by bolts 37 and 38. The extensions 260: are shownin opposed relationship, and between them is the armature 5, and theflanges 34 of arms corresponding to the arms 9 and of Figure 2 andindicated by their body olt 38, the flange portions 26a are p aced Yapart b three thicknesses of metal, namely the thi ness of the armatureand the thickness of the flanges 34 of my magnetic arms lyingon eitherside of the armature. Where t e armature passes between the pole piecesN and S of my'core structure, there will be a-space on either side ofthe armature, determined by the thickness of the flanges 34 between theflanges 26a of my brackets. Thus by grinding true the faces of theassemblies shown in Figure 11, I secure my pole spacing with a greatdegree of accuracy by the simple method just described; and I secure asimilar space at the rear end of my core structure by inserting betweenthe two parts, the blocks 39 shown in Figures 23 and 25. It is thoughtthat the general assembly of my motor will be clear from a considerationof the several figures.

I have shown in Figures 19 and 20 an assembly of my armature 5 and thedrive rod 13. My armature has perforations 40 at its ends for thepassage of the bolts 38. A field coil structure 6a is shown in theseveral figures positioned on the rear portion of my core structure. Thevoice coils are indicated at 7a and 8a, and are illustrated on anenlarged scale in Figures 15 and 16, where it will be seen that in theend flange I produce a oove 41. In my construction, the voice coils areheld spaced apart by the pole pieces N and S in a horizontal direction,and in order that they may not shift in my construction, there is anengagement of the ends of the pole pieces in the notches 41, and theshoulders 22 of my pole pieces engage the flanges of my coils so as tohold them rigidly against motion. This will be clear from aconsideration of Figure 23.

Referring again to Figure 2, I have shown my voice coils 7a and 8apositioned very close to the pole pieces N and S, and separated somedistance from the point of attachment of the arms 9 to 12 to the ends ofmy armature. This construction not only facilitates the rigid holding ofmy voice coils as just described, but it is. also advisable from anoperating standpoint to prevent the return of flux through the air-gapbetween the coils and the adjacent arms, whereby the efiiciency of mymotor might be cut down. To hold my coils against my pole pieces forthis reason, and secure the positive engagement aforesaid, I haveprovided the spring members 42 shown in Figures 17 and 18,

which do not need special description. Their use is illustrated clearlyin Figures 21 and I have thus described in connection with a motor ofthe Hunter and Rockwell type my novel mechanical construction. It willbe clear that this construction may be employed to reduce o rativemotors in accordance wit any of t e several modifications of the Hunterand Rockwell device. For example, one or more of the magnetic arms mayeliminated, while the armature mounting remains the same, and forspacing a smaller piece of metal may be placed against the armature atthe point where it is clam d between brackets 26a in place of the en ofthe magnetic arm. For the reed type of motor, two of the magnetic arms,both being upon the same side of the ole pieces, may be eliminated, areed type of spacing secured by a block of metal between the clampingportions 26a of the brackets on the opposite side of the motor from theside at which the reed armature is mounted. In this type of motorhowever, it is convenient and less expensive to eliminate entirely thebracket members upon the one side of the field structure. Theconstruction of m bracket members and their ri 'dity is suc that two ofthe brackets is sucient to give a satisfactorily rigid and operativestructure. My construction may be employed in cases where there are nomagnetic arms providing return paths for the alternating current flux inthe armature. It will be clear also that modifications in my inventionmay be made to adapt it to different types of motors than the one whichhas been employed herein as an exemplary embodiment of my invention.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent, is 1. In a loud speaker motor, a field corestructure comprislng interspaced pole pieces, a pair of bracketsattached at interspaced points to said field core structure, saidbrackets having clamping members arranged to engage and hold an armaturein a plane such that it will extend between the said pole pieces.

2. In a loud speaker motor, a field core structure in two parts, andbracket members attached to each of said parts, said bracket membershaving clamping faces extending at an angle to the plane of said fieldcore structure and adapted to engage an armature and hold a portion ofsaid armature between interspaced portions of said field core structure.said faces adapted to be interspaced by said armature, and additionalthicknesses of material therebetween so as to interspace said parts ofsaid field core structure.

3. In a loud speaker motor, a field core structure in two parts, a pairof angle brackets attached in opposed position to each of said parts,said angle brackets havin faces substantially coplanar with faces ofsaid field core portions, whereby said field core portions and theattached brackets may be individually worked to make said faces andportions exactly coplanar, said faces adapted to armature employed, and

receive in clampin engagement an interosed armature, an said facesadapted to be mterspaced to control the clearance of said ,armaturebetween parts of said field core portions forming interspaced polepieces.

substantially in the plane of said 4. In a loud speaker motor, a fieldcore structure in two parts adapted to be placed in opposedrelationship, bracket members attached to said parts to hold said partsin oposed relationshi said brackets arranged to e attached toget er,faces on said brackets adapted to clamp an armature between parts ofsaid opposed field core structures, additional material between saidclamping faces to ive clearance to said armature between said parts, andmeans comprising a spacing member between other opposed parts of saidfield core structure to produce a corresponding interspacingtherebetween.

5. In a loud speaker motor, a air of brack ets having faces in planes sustantially at right angles to each other, a pair of field structuresadapted to be attached to one face of each of said brackets, and anarmature structure adapted to be clamped between the other two faces ofsaid brackets, said last mentioned faces being coplanar with faces ofsaid field structure parts. a 6. Ina loud speaker motor, a pair of U-shaped field core structures ada ted to be placed in opposedrelationship to orm a substantially C-shaped core with interspaced polepiece portions, a bracket attached to each of said U-shaped sections,and havin a fgce an a face at substantially right angles thereto, saidface being coplanar with the upper ends of the legs of the U-shapedsection to which it .is attached, portions of said faces adapted toreceive and clamp an armature, and additional thicknesses of metaltherebetween to space said pole pieces on either side of said armature,and said armature therebetween, and a spacing block between the op osedportions of said field structure remote roin said pole pieces.

7. In a loud speaker motor, a pair of U- shaped core sections, bracketson either side .of said core sections, said brackets havingfacessubstantially coplanar with the ends of said core sections and at rightangles to the general plane of said sections, an armature extendingbetween opposed legs and between opposed faces of said clamps, magneticarms one end of which lies between said faces on either side of saidarmature, the other end of which is attached respectively to a leg ofsaid U-shaped section, and means for fastening said faces together.

8. In a loud speaker motor, a pair of U- shaped core sections, bracketson either side of said core sections, said brackets having facessubstantially coplanar with the ends of said core sections and at rightangles to the general plane of said sections, an armature extendingbetween opposed legs and between opposed faces of said clamps, magneticarms one end of which lies between said faces on either sideof saidarmature, the other end of which is attached respectively to a leg ofsaid tween said faces, magnetic arms adapted to be clamped between aface and said armature on one end, and attached to one of said legs onthe other, a field coil surrounding an opposed pair of said legs, aspacer block between said legs, and voice coils on said armature betweensaid legs forming pole pieces and said clamping faces.

10. In a loud speaker motor, a pair of U- shaped core sections, and anangular bracket attached on either side of said core sections and havinga face substantially perpendicular thereto and coplanar with the ends ofsaid sections, said brackets having their angular portions interspacedfrom the legs of said U-shaped sections, said faces adapted to beclamped together to assemble said core sections, an armature adapted tobe clamped between said faces, magnetic arms adapted to be clampedbetween a face and said armature on one end, and attached to one of saidlegs on the other, a field coil surrounding an opposed pair of saidlegs, a spacer block between said legs, and voice coils on said armaturebetween said legs forming pole pieces and said clamping faces, a pair ofsaid brackets having means for mounting said motor on a support.

11. In a loud speaker motor, a pair of U- shaped core sections, and anangular bracket attached on either side of said core sections and havinga face substantially perpendicular thereto and coplanar with the ends ofsaid sections, said brackets having their angular portions interspacedfrom the legs of said U-shaped sections, said faces adapted to beclamped together to assemble said core sections, an armature adapted tobe clamped between said faces, magnetic arms adapted to be clampedbetween a face and said armature on one end, and attached to one of saidlegs on the other, a fieldcoil surrounding an opposed pair of said legs,a spacer block between said legs, and voice coils on said armaturebetween said legs forming pole pieces and said clamping faces, a pair ofsaid brackets having means for mounting said motor on a support, andspring means for holding said voice coils adjacent said legs.

12. In a loud speaker motor, a pair of U- shaped core sections, and anangular bracket attached on either side of said core sections and havinga face substantially per endicular thereto and coplanar with them ofsaid sections, said brackets having their angular portions interspacedfrom the legs of said U-shaped sections, said faces adapted to beclamped together to assemble said core sections, an armature adapted tobe clamped between said faces, magnetic arms adapted to be clampedbetween a face and said armature on one end, and attached to one of saidlegs on the other, a field coil surroundin an opposed pair of said legs,a spacer block tween said legs, and voice coils on said armature betweensaid legs forming pole pieces and said clampin faces, said vo1ce coilshavin shoulders de ning a channel to receive en portions of said legsfor spacing in one direction, said legs having shoulders for spacingsaid coils in another direction, and resilient means for holding saidcoils a inst said legs.

RALPH H. GLEY.

